1. 3.3 Succession: How Ecosystems Change over Time
Unit A
Science 7
Background Information
Succession is a natural process, but it can also be caused by human actions. For example, succession occurs when a new subdivision is built on top of previously forested land. The structural environment is altered drastically when bulldozers clear away all the trees, shrubs, and grasses. A new physical environment consisting of paved roads, concrete buildings, and brick houses replaces the old. Increasing populations of people, along with domesticated animals like dogs and cats, gradually move in and take over the area. Flowering gardens full of nonnative species, tree-lined streets, neatly manicured lawns, and the odd park replace the original forest vegetation. Many of the native species of animals that used to live there, such as deer, snakes, and rabbits cannot tolerate this new environment and either migrate to more suitable locations or die off. Some wild species, however, such as raccoons, skunks, mice, rats, pigeons, and gulls manage to adapt to the new conditions and gradually establish viable populations. The lack of predators and an ample supply of food from human scraps means that some of these creatures do exceptionally well—so well, in fact, that the human inhabitants devote much time and effort trying to get rid of them.

2. Key Terms Pioneer species Succession Primary succession
Climax community
Secondary succession
Prior Knowledge
The concept that forests and wetlands change over time is not new to students. However, the specific concept of succession is new to students.

3. Pioneer Species
Pioneer Species are those organisms, usually plants, that colonize barren rock or lava during primary succession.
Pioneer species physically break up the rocks, extract minerals, and provide organic matter that will decompose and become the soil for later successional species.
Examples of Lichen 

4. Lichens, mosses, ferns, and weeds are often pioneer species
Lichens, mosses, ferns, and weeds are often pioneer species. Lichens can secrete acids that help breakdown rock and provide opportunities for other types of plants to move in.
Growing seedlings can help split boulders weighing more than your family car! Without pioneer species paving the way, ecosystems of a climax community would never develop.
Moss 

5. Give It A Try –p. 62
Look at Figures 3.8 a) – c). Try to decide which one(s) are pioneer species. Explain.
Purpose
To apply the definition of pioneer species to real examples.
Activity Notes
Encourage students to look back at the definition of pioneer species at the top of student book page 62. Have them consider what species look like when they are the first to arrive in a situation where plants were not present earlier. The first and second photos are the pioneer species. In both cases, the plants have moved into an area where there weren’t any other plants. These plants will then “pave the way” for other species by encouraging the development of soil.

6. Succession
Succession is the process of community change and development that happens most obviously when a natural community is disturbed or when new land become available to life. But biological communities are always changing. Many lakes and wetlands gradually become filled in and over thousands of years become dry land.
STARTING THE LESSON
Using the Text
Have students read the three introductory paragraphs on student book page 62. Ask them where they have seen succession occurring in their local area (e.g., vacant lots, sidewalk cracks, unattended field or lawns or parts of them). Which plants do they think are pioneer species in these areas? Have students look at Figures 3.8a)–c) of the Give It a Try Activity to decide if the photos are pioneer species.
Using the i n f oBIT
Students can think about why lichen are a good pioneer species. Have they seen an example in their local area of succession involving lichen? Where?

7. The lake at first (after glaciers formed it) is surrounded by essentially scoured bare land. After a time, pioneer plants establish themselves there. After more time, a forest grows there. Near the shores of the lake grow reeds and cattails and floating mats of sedges, which are cousin to grasses.
Slowly, slowly, generations of sedge-mats die and sink to the bottom of the lake and decompose. After centuries of plant matter building up on the lake bottom, the lake becomes shallower. Given enough time, the lake becomes a cattail marsh or sphagnum peat bog.
Eventually there is no open water left. The lake has transformed from an aquatic community to a wetland community and will eventually become a wet meadow or, further north, a black spruce forest growing on peat.
                                                                                        This muskeg or peat bog was once a lake
Teaching Suggestions
The information on student book page 63 of the text describes two different types of succession: primary succession and secondary succession. As students read through this section, encourage them to think of local examples of the two types of succession. This will help them to remember the differences between the two types of succession. After students have generated several examples of primary and secondary succession, have them work with a group to focus on one specific area and one type of succession and create a poster of the area. Encourage students to focus on what makes
the area an example of primary or secondary succession. Make sure that students provide a complete written description as well as pictures on their poster.

8. Primary Succession
Some succession (primary succession), on the other hand, is the process of life colonizing dead or sterile areas such as volcanic lava flows and new sand dunes, or rock left behind by retreating glaciers, and transforms them into living communities.

9. Secondary Succession
Some succession (secondary succession) is an ecosystem's response to an injury, the way we heal a cut.
Such succession transforms a disturbed or damaged part of a community. Example: a tree falls and creates an opening in the canopy of leaves. Succession fills in the opening.

10. Climax Community
A climax community is a stable group of plants and animals that is the end result of the successional process.

11. Redwood Forest
The redwood forest of California is a climax community. Those trees are huge and can out-compete any invading tree species. The redwoods also provide a stable habitat for other organisms that live in the forest. The redwoods serve as the foundation that supports the rest of the ecosystem. Huge trees are the anchor for literally thousands of other species of organisms.

12. C and R - p. 64
Do all questions.

13. C and R Answers –p.64
1. Students should recognize that plants (or plantlike living things such as lichens) are always the pioneer species. Plants, as producers, must colonize an area before animals can become established because animals, being consumers, need producers to feed on.
2. Answers will vary, but students may identify stages like those below (for primary succession). Encourage students to provide as much detail as possible for each stage. Look in particular for evidence of their understanding that pioneer species must be producers, and are usually small and low-growing.
a) bare rock
b) rock covered with lichens
c) mosses and other small plants growing in the developing soil
d) grasses and small shrubs/bushes growing in more developed soil
e) trees growing in fully developed soil.
Note: for grasslands, the climax community will be d.
1. Students should recognize that plants (or plantlike living things such as lichens) are always the pioneer species. Plants, as producers, must colonize an area before animals can become established because animals, being consumers, need producers to feed on.
2. Answers will vary, but students may identify stages like those below (for primary succession). Encourage students to provide as much detail as possible for each stage. Look in particular for evidence of their understanding that pioneer species must be producers, and are usually small and low-growing.
a) bare rock
b) rock covered with lichens
c) mosses and other small plants growing in the developing soil
d) grasses and small shrubs/bushes growing in more developed soil
e) trees growing in fully developed soil.
Note: for grasslands, the climax community will be d.
3. In primary succession, a new community develops in an area where no community existed before. In secondary succession, a new community develops in an area where a previously existing community has been disturbed or destroyed by natural or human activity.
4. Students may suggest lichens, ferns, or mosses for pioneer species. For climax species, they may suggest any large trees such as pine, spruce, or poplar. However, if they are describing grasslands, they should suggest grasses or shrubs, not large trees.
5. The most logical sequence is fireweed, grass, mouse, birch tree, bear. Ask students to identify this sequence as an example of primary or secondary succession, with reasons.
6. These photos would be an example of secondary succession. Because the land is no longer being used for farming, native plants, shrubs, and trees have moved back to re-establish themselves. Students should be able to find many examples in their communities. They just need to look at the
edge of the schoolyard or open lot to see examples of plants that are re-establishing themselves.

14. C and R Answers –p.64
3. In primary succession, a new community develops in an area where no community existed before. In secondary succession, a new community develops in an area where a previously existing community has been disturbed or destroyed by natural or human activity.
4. Students may suggest lichens, ferns, or mosses for pioneer species. For climax species, they may suggest any large trees such as pine, spruce, or poplar. However, if they are describing grasslands, they should suggest grasses or shrubs, not large trees.
1. Students should recognize that plants (or plantlike living things such as lichens) are always the pioneer species. Plants, as producers, must colonize an area before animals can become established because animals, being consumers, need producers to feed on.
2. Answers will vary, but students may identify stages like those below (for primary succession). Encourage students to provide as much detail as possible for each stage. Look in particular for evidence of their understanding that pioneer species must be producers, and are usually small and low-growing.
a) bare rock
b) rock covered with lichens
c) mosses and other small plants growing in the developing soil
d) grasses and small shrubs/bushes growing in more developed soil
e) trees growing in fully developed soil.
Note: for grasslands, the climax community will be d.
3. In primary succession, a new community develops in an area where no community existed before. In secondary succession, a new community develops in an area where a previously existing community has been disturbed or destroyed by natural or human activity.
4. Students may suggest lichens, ferns, or mosses for pioneer species. For climax species, they may suggest any large trees such as pine, spruce, or poplar. However, if they are describing grasslands, they should suggest grasses or shrubs, not large trees.
5. The most logical sequence is fireweed, grass, mouse, birch tree, bear. Ask students to identify this sequence as an example of primary or secondary succession, with reasons.
6. These photos would be an example of secondary succession. Because the land is no longer being used for farming, native plants, shrubs, and trees have moved back to re-establish themselves. Students should be able to find many examples in their communities. They just need to look at the
edge of the schoolyard or open lot to see examples of plants that are re-establishing themselves.

15. C and R Answers –p.64
5. The most logical sequence is fireweed, grass, mouse, birch tree, bear. Ask students to identify this sequence as an example of primary or secondary succession, with reasons.
6. These photos would be an example of secondary succession. Because the land is no longer being used for farming, native plants, shrubs, and trees have moved back to re-establish themselves. Students should be able to find many examples in their communities. They just need to look at the edge of the schoolyard or open lot to see examples of plants that are re-establishing themselves.
1. Students should recognize that plants (or plantlike living things such as lichens) are always the pioneer species. Plants, as producers, must colonize an area before animals can become established because animals, being consumers, need producers to feed on.
2. Answers will vary, but students may identify stages like those below (for primary succession). Encourage students to provide as much detail as possible for each stage. Look in particular for evidence of their understanding that pioneer species must be producers, and are usually small and low-growing.
a) bare rock
b) rock covered with lichens
c) mosses and other small plants growing in the developing soil
d) grasses and small shrubs/bushes growing in more developed soil
e) trees growing in fully developed soil.
Note: for grasslands, the climax community will be d.
3. In primary succession, a new community develops in an area where no community existed before. In secondary succession, a new community develops in an area where a previously existing community has been disturbed or destroyed by natural or human activity.
4. Students may suggest lichens, ferns, or mosses for pioneer species. For climax species, they may suggest any large trees such as pine, spruce, or poplar. However, if they are describing grasslands, they should suggest grasses or shrubs, not large trees.
5. The most logical sequence is fireweed, grass, mouse, birch tree, bear. Ask students to identify this sequence as an example of primary or secondary succession, with reasons.
6. These photos would be an example of secondary succession. Because the land is no longer being used for farming, native plants, shrubs, and trees have moved back to re-establish themselves. Students should be able to find many examples in their communities. They just need to look at the
edge of the schoolyard or open lot to see examples of plants that are re-establishing themselves.

16. AYL – p. 65
Do All Questions

17. AYL Answers –p.65
1. a) Students may suggest floods, drought, tornadoes, hurricanes, or other violent weather-related events.
b) The details students provide will vary, but most answers will likely focus on loss (or reduced numbers) of producer and/or consumer populations, and the effects of those losses or reductions (e.g., an increase in other populations, which might eventually lead to further reductions if food becomes scarce). Students should provide sufficient detail to explain the causes and effects they identify.
SECTION REVIEW
Assess Your Learning
1. a) Students may suggest floods, drought, tornadoes, hurricanes, or other violent weather-related events.
b) The details students provide will vary, but most answers will likely focus on loss (or reduced numbers) of producer and/or consumer populations,
and the effects of those losses or reductions (e.g., an increase in other populations, which might eventually lead to further reductions if food becomes
scarce). Students should provide sufficient detail to explain the causes and effects they identify.
2. Answers will vary but illustrations or written work should be accurate and clearly show how primary succession takes place. Primary succession begins with the arrival of a plant to an area that has not had any life before. Over time, this pioneer plant helps to break down rocks into soil. As the soil becomes more fertile, other plants move in.
3. Population fluctuations can cause many changes in an ecosystem. For example, with the lynx/hare cycle, an increase in the food supply for the hares means that more hares survive. When more hares survive, more lynx can survive. However, when the hares decimate their food supply, their numbers will decrease and then so will the lynx numbers. The populations of organisms are closely connected through the food chains.
4. Answers will vary. However, some of the following interactions can cause changes in an ecosystem: predation, human impact, bioinvasion, and resource competition.
5. Student examples may vary, but secondary succession can occur in any ecosystem where a community has been destroyed by natural occurrences or human activities.
6. Answers will vary. However, students could expect that removal of the bears would cause significant changes in the ecosystem, because they are an important part of the food chain. Students’ plans could list measuring the biotic factors before the bears were removed and then after the bears were removed. Students’ plans may also provide a specific example of how the removal of the bears will affect all the organisms in the park.

18. AYL Answers –p.65
2. Answers will vary but illustrations or written work should be accurate and clearly show how primary succession takes place. Primary succession begins with the arrival of a plant to an area that has not had any life before. Over time, this pioneer plant helps to break down rocks into soil. As the soil becomes more fertile, other plants move in.
SECTION REVIEW
Assess Your Learning
1. a) Students may suggest floods, drought, tornadoes, hurricanes, or other violent weather-related events.
b) The details students provide will vary, but most answers will likely focus on loss (or reduced numbers) of producer and/or consumer populations,
and the effects of those losses or reductions (e.g., an increase in other populations, which might eventually lead to further reductions if food becomes
scarce). Students should provide sufficient detail to explain the causes and effects they identify.
2. Answers will vary but illustrations or written work should be accurate and clearly show how primary succession takes place. Primary succession begins with the arrival of a plant to an area that has not had any life before. Over time, this pioneer plant helps to break down rocks into soil. As the soil becomes more fertile, other plants move in.
3. Population fluctuations can cause many changes in an ecosystem. For example, with the lynx/hare cycle, an increase in the food supply for the hares means that more hares survive. When more hares survive, more lynx can survive. However, when the hares decimate their food supply, their numbers will decrease and then so will the lynx numbers. The populations of organisms are closely connected through the food chains.
4. Answers will vary. However, some of the following interactions can cause changes in an ecosystem: predation, human impact, bioinvasion, and resource competition.
5. Student examples may vary, but secondary succession can occur in any ecosystem where a community has been destroyed by natural occurrences or human activities.
6. Answers will vary. However, students could expect that removal of the bears would cause significant changes in the ecosystem, because they are an important part of the food chain. Students’ plans could list measuring the biotic factors before the bears were removed and then after the bears were removed. Students’ plans may also provide a specific example of how the removal of the bears will affect all the organisms in the park.

19. AYL Answers –p.65
3. Population fluctuations can cause many changes in an ecosystem. For example, with the lynx/hare cycle, an increase in the food supply for the hares means that more hares survive. When more hares survive, more lynx can survive. However, when the hares decimate their food supply, their numbers will decrease and then so will the lynx numbers. The populations of organisms are closely connected through the food chains.
4. Some of the following interactions can cause changes in an ecosystem: predation, human impact, bioinvasion, and resource competition.
SECTION REVIEW
Assess Your Learning
1. a) Students may suggest floods, drought, tornadoes, hurricanes, or other violent weather-related events.
b) The details students provide will vary, but most answers will likely focus on loss (or reduced numbers) of producer and/or consumer populations,
and the effects of those losses or reductions (e.g., an increase in other populations, which might eventually lead to further reductions if food becomes
scarce). Students should provide sufficient detail to explain the causes and effects they identify.
2. Answers will vary but illustrations or written work should be accurate and clearly show how primary succession takes place. Primary succession begins with the arrival of a plant to an area that has not had any life before. Over time, this pioneer plant helps to break down rocks into soil. As the soil becomes more fertile, other plants move in.
3. Population fluctuations can cause many changes in an ecosystem. For example, with the lynx/hare cycle, an increase in the food supply for the hares means that more hares survive. When more hares survive, more lynx can survive. However, when the hares decimate their food supply, their numbers will decrease and then so will the lynx numbers. The populations of organisms are closely connected through the food chains.
4. Answers will vary. However, some of the following interactions can cause changes in an ecosystem: predation, human impact, bioinvasion, and resource competition.
5. Student examples may vary, but secondary succession can occur in any ecosystem where a community has been destroyed by natural occurrences or human activities.
6. Answers will vary. However, students could expect that removal of the bears would cause significant changes in the ecosystem, because they are an important part of the food chain. Students’ plans could list measuring the biotic factors before the bears were removed and then after the bears were removed. Students’ plans may also provide a specific example of how the removal of the bears will affect all the organisms in the park.

20. AYL Answers –p.65
5. Secondary succession can occur in any ecosystem where a community has been destroyed by natural occurrences or human activities.
6. The removal of the bears would cause significant changes in the ecosystem, because they are an important part of the food chain. Students’ plans could list measuring the biotic factors before the bears were removed and then after the bears were removed. Students’ plans may also provide a specific example of how the removal of the bears will affect all the organisms in the park.
SECTION REVIEW
Assess Your Learning
1. a) Students may suggest floods, drought, tornadoes, hurricanes, or other violent weather-related events.
b) The details students provide will vary, but most answers will likely focus on loss (or reduced numbers) of producer and/or consumer populations,
and the effects of those losses or reductions (e.g., an increase in other populations, which might eventually lead to further reductions if food becomes
scarce). Students should provide sufficient detail to explain the causes and effects they identify.
2. Answers will vary but illustrations or written work should be accurate and clearly show how primary succession takes place. Primary succession begins with the arrival of a plant to an area that has not had any life before. Over time, this pioneer plant helps to break down rocks into soil. As the soil becomes more fertile, other plants move in.
3. Population fluctuations can cause many changes in an ecosystem. For example, with the lynx/hare cycle, an increase in the food supply for the hares means that more hares survive. When more hares survive, more lynx can survive. However, when the hares decimate their food supply, their numbers will decrease and then so will the lynx numbers. The populations of organisms are closely connected through the food chains.
4. Answers will vary. However, some of the following interactions can cause changes in an ecosystem: predation, human impact, bioinvasion, and resource competition.
5. Student examples may vary, but secondary succession can occur in any ecosystem where a community has been destroyed by natural occurrences or human activities.
6. Answers will vary. However, students could expect that removal of the bears would cause significant changes in the ecosystem, because they are an important part of the food chain. Students’ plans could list measuring the biotic factors before the bears were removed and then after the bears were removed. Students’ plans may also provide a specific example of how the removal of the bears will affect all the organisms in the park.

21. Review Key Terms Pioneer species Succession Primary succession
Climax community
Secondary succession